Question

如果cos2x=3/5.那么sin^4+cos^4x=多少

Answer 1

(sinx)^4+(cosx)^4

=[(sinx)^2+(cosx)^2]^2-2(sinx)^2(cosx)^2

=1-(1/2)[sin(2x)]^2

=1-(1/2)[1-cos(2x)^2]

=1-(1/2)[1-(3/5)^2]

=1-8/25

=17/25